Loudspeaker



Dec. 16, 1969 HIROMI SOTOME 3,483,946

LOUDSPEAKER Filed Dec. 26, 1968 2 Sheets-Sheet l FIG.1

INVENTOR H/KD Y DTP/1E ATTORNEY S Dec. 16, 1969 HIROMI SOTOME 3,483,946

LOUDSPEAKER Filed Dec. 26, 1968 2 Sheets-Sheet 2 FIG. 3

INVENTOR H IROHI JDTDHE ATTORNEYS United States Patent Ofice 3,483,946 Patented Dec. 16, 1969 3,483,946 LOUDSPEAKER Hiromi Sotome, Hamamatsu-shi, Japan, assignor to Nippon Gakki Seizo Kabushiki Kaisha, Hamamatsu-slii,

US. Cl. 181-32 1 Claim ABSTRACT OF THE DISCLOSURE A loudspeaker including a diaphragm made of substantially fiat plate of plastic, foamed plastic or the like material which is clamped at'its periphery on a speaker frame so as to produce sounds by bending motion of said diaphragm, characterized in that said diaphragm is formed to have an asymmetric contour at its periphery as seen from its front side and a conical configuration at its central driven portion, said conical configuration being formed in an asymmetric shape corresponding to the asymmetric contour of the periphery of the diaphragm.

BACKGROUND OF THE INVENTION The present invention relates to a loudspeaker of the type including a diaphragm made of a substantially flat plate of plastic, foamed plastic such as foamed polystyrene or the like material which is clamped at its periphery on a speaker frame so as to produce sounds by bending motion of said diaphragm.

In the diaphragm of the above type, the diaphragm tends to produce divided vibrations, so that excessive resonance may occur at particular frequencies, resulting turbulence in frequency characteristics of the loudspeaker.

In order to prevent the turbulence in frequency characteristics it has been proposed to use a diaphragm having an asymmetric contour as seen from its front side. In such an asymmetric diaphragm, vibration mode appears in complication form, so that large peaks and dips are not likely to occur in frequency characteristics. It has been also proposed to increase the flexural rigidity of the diaphragm at its central driven area by making said area in a conical form. In such a construction the divided mode is not likely to occur, thus improving the frequency characteristics of the loudspeaker.

Thus the diaphragm having an asymmetric contour at its periphery as seen from its front side and a conical shape at its central driven portion as seen in section has been proposed, which has obtained an improvement in frequency characteristics as compared with the conventional loudspeaker having flat-plate type diaphragm.

It has been found, however, that in the asymmetric construction heretofore proposed a relatively large flat portion is formed between the periphery of the diaphragm and the outer end of the conical portion thereof, said fiat portion having a reduced flexural rigidity, so that an extreme divided vibration can occur at this flat portion, thus producing turbulence or excessive peaks and dips in the frequency characteristics, particularly in the middle and low frequency ranges.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a loudspeaker having a flat-plate type diaphragm in which the above-mentioned defect in the asymmetric construction is eliminated, thus obtaining improved frequency characteristics.

In accordance with the present invention there is provided a loudspeaker including a diaphragm made of substantially flat plate clamped at its periphery on a speaker frame so as to produce sounds by bending motion of said diaphragm, said diaphragm 'being formed to have an asymmetric contour at its periphery as seen from its front side and a conical configuration at its central driven portion, said conical configuration being formed in an asymmetric form correspoding to the asymmetric contour of the periphery of the diaphragm.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view showing an example of a loud speaker according to a prior art;

FIG. 2 is a sectional view taken along line IIII in FIG. 1;

FIG. 3 is a front view showing an embodiment of the present invention; and

FIG. 4 is a sectional view taken along line IV1V in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIGS. 1 and 2 show an example of a loudspeaker according to a prior art, which comprises a substantially fiat diaphragm 1 made of foamed polystyrene or the like material, a speaker frame 2, a magnetic circuit 3 and a voice coil 4, said diaphragm 1 being clamped at its periphery on said speaker frame 2 by a suitable means such as adhesive agent. The diaphragm 1 is formed in an asymmetric contour at its periphery as seen from front side thereof and in a conical configuration at its central portion 5 which is to be driven by the voice coil 4.

Heretofore it has been a usual practice to form said conical portion 5 in a circular or elliptical symmetric form, as shown by contour lines 6 in FIG. 1. In such a construction a flat portion exists between the periphery of the diaphragm and the outer end 7 of the conical portion 5. Since the diaphragm is formed in an asymmetric contour at its periphery, a relatively large flat portion is formed in the direction of larger radius of the diaphragm, as shown by circular broken lines 8 in FIG. 1. Such portion has a reduced flexural rigidity, so that an undesirable divided vibration can occur, thus producing excessive peaks and dips in the frequency characteristics particularly in the intermediate and low frequency ranges.

FIGS. 3 and 4 illustrate an embodiment of the present invention, which comprises a diaphragm 11 made of foamed polystyrene or the like material, a speaker frame 12, a magnetic circuit 13 and a voice coil 14, said diaphragm 11 being clamped at its periphery on the frame 12 by suitable means, such as adhesive agent.

The diaphragm 11 is formed in an asymmetric contour at its periphery as seen from its front side and in a conical configuration at its central portion 15 which is to be driven by the voice coil 14. The conical portion 15 is formed in an asymmetric form corresponding to the asymmetric contour corresponding to the asymmetric shape of the periphery of the diaphragm, as shown by contour lines 16 in FIG. 3.

In the above construction of the diaphragm, a flat portion of substantially uniform width is formed between the periphery of the diaphragm and the outer end 17 of the conical portion 15 according to the asymmetric contour of the periphery of the diaphragm, and a large flat portion such as shown by broken lines 8 in FIG. 1 is not formed at any part of the diaphragm. Accordingly a remarkable improvement can be obtained in the frequency characteristics.

It should be noted, however, that if the diaphragm is formed entirely in a conical form from the central driven portion to the clamped periphery the flexural rigidity of the diaphragm is so increased that it becomes impossible to lower the lowest resonance frequency f of the loudspeaker and, therefore, a substantial fiat portion should 'be retained between the periphery and the outer end of the conical portion.

I claim:

1. A loudspeaker including a diaphragm made of substantially fiat plate clamped at its periphery on a speaker frame so as to produce sounds by bending motion of said diaphragm, said diaphragm being formed to have an asymmetric contour at its periphery as seen from its front side and a conical configuration at its central driven portion, said conical configuration being formed in an a l, Q43 v asymmetric form corresponding to the asymmetric contour of the periphery of the diaphragm.

References Cited UNITED STATES PATENTS 3,111,189 11/1963 Scholl 181-32 3,172,498 3/1965 Gorike 18132 3,180,945 4/1965 Suzuki 179-115 3,247,925 4/1966 Warnaka 181'31 STEPHEN J. TOMSKY; Primary Examiner 

